In a conventional vehicle using ethanol-mixed gasoline, ethanol density contained in fuel is detected so as to adjust fuel injection amount as well as fuel injection timing in accordance with detected ethanol density, so that deterioration of exhaust gas is suppressed and adverse affect to vehicle drivability is decreased.
According to a prior art, such as U.S. Pat. No. 7,030,629, electrostatic capacity between a first electrode forming a fluid passageway and a second electrode supported within the fluid passageway is detected, and ethanol density contained in fuel is detected based on detected value for the electrostatic capacity, wherein the detected value for the electrostatic capacity is corrected by fuel temperature detected by a temperature sensor.
According to such a fluid quality sensor, however, heat generated at an electric circuit for detecting the ethanol density as well as heat from ambient atmosphere may be transmitted to the temperature sensor through an inside of a sensor housing. Therefore, there is a concern that such heat transfer may adversely affect detection value of the temperature sensor. In the case that an error may occur in the detection value, detection accuracy for the ethanol density may be decreased.
In addition, there may be another concern that a glass seal for insulating between the first and second electrodes may be broken or a crack may be generated in the glass seal, for example, due to mechanical shock during product transportation or a product assembling process. When the glass seal was broken, there would be a possibility that fuel may leak from the fuel passageway.
Furthermore, there is a concern that electric conductive members, which connect the first and second electrodes and the electric circuit with each other, may be disconnected due to different coefficients of thermal expansion between the housing for the electric circuit and the first and second electrodes. In such a case (disconnection of electric conductive members), it becomes impossible to detect the electrostatic capacity.